Method and apparatus for transmitting power headroom report in wireless communication system

ABSTRACT

A method and apparatus for transmitting a power headroom report (PHR) in a wireless communication system is provided. A user equipment (UE) transmits a first PHR for a first carrier group, which is configured by a first eNodeB (eNB), to a second eNB; and transmitting a second PHR for a second carrier group, which is configured by the second eNB, to the first eNB. The first PHR and the second PHR include a PHR for a physical uplink control channel (PUCCH) regardless of whether simultaneous transmission of the PUCCH and a physical uplink shared channel (PUSCH) is configured or not.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/787,028, filed on Oct. 18, 2017, now U.S. Pat. No. 10,390,310, whichis a continuation of U.S. patent application Ser. No. 14/912,832, filedon Feb. 18, 2016, now U.S. Pat. No. 9,838,982, which is the NationalStage filing under 35 U.S.C. 371 of International Application No.PCT/KR2014/008344, filed on Sep. 4, 2014, which claims the benefit ofU.S. Provisional Application No. 61/873,804, filed on Sep. 4, 2013,61/927,503, filed on Jan. 15, 2014, 61/938,147, filed on Feb. 11, 2014,61/940,379, filed on Feb. 15, 2014, 61/943,457, filed on Feb. 23, 2014,61/976,486, filed on Apr. 7, 2014, 61/981,170, filed on Apr. 17, 2014,61/984,030, filed on Apr. 24, 2014, 62/009,311, filed on Jun. 8, 2014,62/014,120, filed on Jun. 19, 2014, 62/015,505, filed on Jun. 22, 2014,62/033,630, filed on Aug. 5, 2014 and 62/034,153 filed on Aug. 7, 2014,the contents of which are all hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for transmitting a powerheadroom report in a wireless communication system.

Related Art

Universal mobile telecommunications system (UMTS) is a 3^(rd) generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). A long-term evolution (LTE) of UMTS is under discussion by the3^(rd) generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

To increase the capacity for the users' demand of services, increasingthe bandwidth may be essential, a carrier aggregation (CA) technology orresource aggregation over intra-node carriers or inter-node carriersaiming at obtaining an effect, as if a logically wider band is used, bygrouping a plurality of physically non-continuous bands in a frequencydomain has been developed to effectively use fragmented small bands.Individual unit carriers grouped by carrier aggregation is known as acomponent carrier (CC). For inter-node resource aggregation, for eachnode, carrier group (CG) can be established here one CG can havemultiple CCs. Each CC is defined by a single bandwidth and a centerfrequency.

In LTE Rel-12, a new study on small cell enhancement has started, wheredual connectivity is supported. Dual connectivity is an operation wherea given UE consumes radio resources provided by at least two differentnetwork points (master eNB (MeNB) and secondary eNB (SeNB)) connectedwith non-ideal backhaul while in RRC_CONNECTED. Furthermore, each eNBinvolved in dual connectivity for a UE may assume different roles. Thoseroles do not necessarily depend on the eNB's power class and can varyamong UEs.

The power headroom reporting (PHR) procedure is used to provide theserving eNB with information about the difference between the nominal UEmaximum transmit power and the estimated power for uplink shared channel(UL-SCH) transmission per activated serving cell and also withinformation about the difference between the nominal UE maximum powerand the estimated power for UL-SCH and PUCCH transmission on primarycell (PCell). Efficient power headroom reporting method for CA or dualconnectivity may be required.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for transmitting apower headroom report (PHR) in a wireless communication system. Thepresent invention provides a method for a method for transmitting thesame type of PHR for a plurality of carrier groups regardless of whethersimultaneous transmission of a physical uplink control channel (PUCCH)and a physical shared channel (PUSCH) is configured or not.

In an aspect, a method for transmitting, by a user equipment (UE), apower headroom report (PHR) in a wireless communication system isprovided. The method includes transmitting a first PHR for a firstcarrier group, which is configured by a first eNodeB (eNB), to a secondeNB, and transmitting a second PHR for a second carrier group, which isconfigured by the second eNB, to the first eNB. The first PHR and thesecond PHR include a PHR for a physical uplink control channel (PUCCH)regardless of whether simultaneous transmission of the PUCCH and aphysical uplink shared channel (PUSCH) is configured or not.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a radio frequency (RF) unit fortransmitting or receiving a radio signal, and a processor coupled to theRF unit, and configured to transmit a first PHR for a first carriergroup, which is configured by a first eNodeB (eNB), to a second eNB, andtransmit a second PHR for a second carrier group, which is configured bythe second eNB, to the first eNB. The first PHR and the second PHRinclude a PHR for a physical uplink control channel (PUCCH) regardlessof whether simultaneous transmission of the PUCCH and a physical uplinkshared channel (PUSCH) is configured or not.

A PHR can be transmitted efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows structure of a radio frame of 3GPP LTE.

FIG. 3 shows a resource grid for one downlink slot.

FIG. 4 shows structure of a downlink subframe.

FIG. 5 shows structure of an uplink subframe.

FIG. 6 shows an example of a carrier aggregation of 3GPP LTE-A.

FIG. 7 shows an example of dual connectivity to a macro cell and a smallcell.

FIG. 8 shows a power headroom MAC CE.

FIG. 9 shows an extended power headroom MAC CE.

FIG. 10 shows an example of a method for transmitting a PHR according toan embodiment of the present invention.

FIG. 11 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Techniques, apparatus and systems described herein may be used invarious wireless access technologies such as code division multipleaccess (CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), single carrier frequency division multiple access (SC-FDMA),etc. The CDMA may be implemented with a radio technology such asuniversal terrestrial radio access (UTRA) or CDMA2000. The TDMA may beimplemented with a radio technology such as global system for mobilecommunications (GSM)/general packet radio service (GPRS)/enhanced datarates for GSM evolution (EDGE). The OFDMA may be implemented with aradio technology such as institute of electrical and electronicsengineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20,evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobiletelecommunication system (UMTS). 3rd generation partnership project(3GPP) long term evolution (LTE) is a part of an evolved-UMTS (E-UMTS)using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink and employsthe SC-FDMA in uplink. LTE-advance (LTE-A) is an evolution of the 3GPPLTE. For clarity, this application focuses on the 3GPP LTE/LTE-A.However, technical features of the present invention are not limitedthereto.

FIG. 1 shows a wireless communication system. The wireless communicationsystem 10 includes at least one base station (BS) 11. Respective BSs 11provide a communication service to particular geographical areas 15 a,15 b, and 15 c (which are generally called cells). Each cell may bedivided into a plurality of areas (which are called sectors). A userequipment (UE) 12 may be fixed or mobile and may be referred to by othernames such as mobile station (MS), mobile terminal (MT), user terminal(UT), subscriber station (SS), wireless device, personal digitalassistant (PDA), wireless modem, handheld device. The BS 11 generallyrefers to a fixed station that communicates with the UE 12 and may becalled by other names such as evolved-NodeB (eNB), base transceiversystem (BTS), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. ABS providing a communication service to theserving cell is called a serving BS. The wireless communication systemis a cellular system, so a different cell adjacent to the serving cellexists. The different cell adjacent to the serving cell is called aneighbor cell. A BS providing a communication service to the neighborcell is called a neighbor BS. The serving cell and the neighbor cell arerelatively determined based on a UE.

This technique can be used for downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS 11. In downlink, a transmittermay be part of the BS 11 and a receiver may be part of the UE 12. Inuplink, a transmitter may be part of the UE 12 and a receiver may bepart of the BS 11.

The wireless communication system may be any one of a multiple-inputmultiple-output (MIMO) system, a multiple-input single-output (MISO)system, a single-input single-output (SISO) system, and a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmission antennas and a plurality of reception antennas. The MISOsystem uses a plurality of transmission antennas and a single receptionantenna. The SISO system uses a single transmission antenna and a singlereception antenna. The SIMO system uses a single transmission antennaand a plurality of reception antennas. Hereinafter, a transmissionantenna refers to a physical or logical antenna used for transmitting asignal or a stream, and a reception antenna refers to a physical orlogical antenna used for receiving a signal or a stream.

FIG. 2 shows structure of a radio frame of 3GPP LTE. Referring to FIG.2, a radio frame includes 10 subframes. A subframe includes two slots intime domain. A time for transmitting one subframe is defined as atransmission time interval (TTI). For example, one subframe may have alength of 1 millisecond (ms), and one slot may have a length of 0.5 ms.One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in time domain. Since the 3GPP LTE uses theOFDMA in the downlink, the OFDM symbol is for representing one symbolperiod. The OFDM symbols may be called by other names depending on amultiple-access scheme. For example, when SC-FDMA is in use as an uplinkmulti-access scheme, the OFDM symbols may be called SC-FDMA symbols. Aresource block (RB) is a resource allocation unit, and includes aplurality of contiguous subcarriers in one slot. The structure of theradio frame is shown for exemplary purposes only. Thus, the number ofsubframes included in the radio frame or the number of slots included inthe subframe or the number of OFDM symbols included in the slot may bemodified in various manners.

3GPP LTE defines that one slot includes seven OFDM symbols in a normalcyclic prefix (CP) and one slot includes six OFDM symbols in an extendedCP.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, an uplink transmission and a downlinktransmission are made at different frequency bands. According to the TDDscheme, an uplink transmission and a downlink transmission are madeduring different periods of time at the same frequency band. A channelresponse of the TDD scheme is substantially reciprocal. This means thata downlink channel response and an uplink channel response are almostthe same in a given frequency band. Thus, the TDD-based wirelesscommunication system is advantageous in that the downlink channelresponse can be obtained from the uplink channel response. In the TDDscheme, the entire frequency band is time-divided for uplink anddownlink transmissions, so a downlink transmission by the BS and anuplink transmission by the UE cannot be simultaneously performed. In aTDD system in which an uplink transmission and a downlink transmissionare discriminated in units of subframes, the uplink transmission and thedownlink transmission are performed in different subframes.

FIG. 3 shows a resource grid for one downlink slot. Referring to FIG. 3,a downlink slot includes a plurality of OFDM symbols in time domain. Itis described herein that one downlink slot includes 7 OFDM symbols, andone RB includes 12 subcarriers in frequency domain as an example.However, the present invention is not limited thereto. Each element onthe resource grid is referred to as a resource element (RE). One RBincludes 12×7 resource elements. The number N^(DL) of RBs included inthe downlink slot depends on a downlink transmit bandwidth. Thestructure of an uplink slot may be same as that of the downlink slot.

The number of OFDM symbols and the number of subcarriers may varydepending on the length of a CP, frequency spacing, and the like. Forexample, in case of a normal CP, the number of OFDM symbols is 7, and incase of an extended CP, the number of OFDM symbols is 6. One of 128,256, 512, 1024, 1536, and 2048 may be selectively used as the number ofsubcarriers in one OFDM symbol.

FIG. 4 shows structure of a downlink subframe. Referring to FIG. 4, amaximum of three OFDM symbols located in a front portion of a first slotwithin a subframe correspond to a control region to be assigned with acontrol channel. The remaining OFDM symbols correspond to a data regionto be assigned with a physical downlink shared chancel (PDSCH). Examplesof downlink control channels used in the 3GPP LTE includes a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe and carries information regarding the numberof OFDM symbols used for transmission of control channels within thesubframe. The PHICH is a response of uplink transmission and carries anHARQ acknowledgment (ACK)/non-acknowledgment (NACK) signal. Controlinformation transmitted through the PDCCH is referred to as downlinkcontrol information (DCI). The DCI includes uplink or downlinkscheduling information or includes an uplink transmit (Tx) power controlcommand for arbitrary UE groups.

The PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, a resource allocation of anupper-layer control message such as a random access response transmittedon the PDSCH, a set of Tx power control commands on individual UEswithin an arbitrary UE group, a Tx power control command, activation ofa voice over IP (VoIP), etc. A plurality of PDCCHs can be transmittedwithin a control region. The UE can monitor the plurality of PDCCHs. ThePDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups.

A format of the PDCCH and the number of bits of the available PDCCH aredetermined according to a correlation between the number of CCEs and thecoding rate provided by the CCEs. The BS determines a PDCCH formataccording to a DCI to be transmitted to the UE, and attaches a cyclicredundancy check (CRC) to control information. The CRC is masked with aunique identifier (referred to as a radio network temporary identifier(RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is fora specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UEmay be masked to the CRC. Alternatively, if the PDCCH is for a pagingmessage, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) maybe masked to the CRC. If the PDCCH is for system information (morespecifically, a system information block (SIB) to be described below), asystem information identifier and a system information RNTI (SI-RNTI)may be masked to the CRC. To indicate a random access response that is aresponse for transmission of a random access preamble of the UE, arandom access-RNTI (RA-RNTI) may be masked to the CRC.

FIG. 5 shows structure of an uplink subframe. Referring to FIG. 5, anuplink subframe can be divided in a frequency domain into a controlregion and a data region. The control region is allocated with aphysical uplink control channel (PUCCH) for carrying uplink controlinformation. The data region is allocated with a physical uplink sharedchannel (PUSCH) for carrying user data. When indicated by a higherlayer, the UE may support a simultaneous transmission of the PUSCH andthe PUCCH. The PUCCH for one UE is allocated to an RB pair in asubframe. RBs belonging to the RB pair occupy different subcarriers inrespective two slots. This is called that the RB pair allocated to thePUCCH is frequency-hopped in a slot boundary. This is said that the pairof RBs allocated to the PUCCH is frequency-hopped at the slot boundary.The UE can obtain a frequency diversity gain by transmitting uplinkcontrol information through different subcarriers according to time.

Uplink control information transmitted on the PUCCH may include a hybridautomatic repeat request (HARQ) acknowledgement/non-acknowledgement(ACK/NACK), a channel quality indicator (CQI) indicating the state of adownlink channel, a scheduling request (SR), and the like.

The PUSCH is mapped to an uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

Carrier aggregation (CA) is described. It may be referred to Section 5.5of 3GPP TS 36.300 V11.6.0 (2013-06).

In CA, two or more component carriers (CCs) are aggregated in order tosupport wider transmission bandwidths up to 100 MHz or more. A UE maysimultaneously receive or transmit on one or multiple CCs depending onits capabilities. A UE with single timing advance capability for CA cansimultaneously receive and/or transmit on multiple CCs corresponding tomultiple serving cells sharing the same timing advance (multiple servingcells grouped in one timing advance group (TAG)). A UE with multipletiming advance capability for CA can simultaneously receive and/ortransmit on multiple CCs corresponding to multiple serving cells withdifferent timing advances (multiple serving cells grouped in multipleTAGs). E-UTRAN ensures that each TAG contains at least one serving cell.A non-CA capable UE can receive on a single CC and transmit on a singleCC corresponding to one serving cell only (one serving cell in one TAG).

A serving cell is combination of downlink and optionally uplinkresources. That is, a serving cell may consist of one DL CC and one ULCC. Alternatively, a serving cell may consist of one DL CC. CA may havea plurality of serving cells. The plurality of serving cells may consistof one primary serving cell (PCell) and at least one secondary servingcell (SCell). PUCCH transmission, random access procedure, etc., may beperformed only in the PCell.

FIG. 6 shows an example of a carrier aggregation of 3GPP LTE-A.Referring to FIG. 6, each CC has a bandwidth of 20 MHz, which is abandwidth of 3GPP LTE. Up to 5 CCs or more may be aggregated, so maximumbandwidth of 100 MHz or more may be configured.

CA is supported for both contiguous and non-contiguous CCs with each CClimited to a maximum of 110 RBs in the frequency domain using theRel-8/9 numerology.

It is possible to configure a UE to aggregate a different number of CCsoriginating from the same eNB and of possibly different bandwidths inthe UL and the DL. The number of DL CCs that can be configured dependson the DL aggregation capability of the UE. The number of UL CCs thatcan be configured depends on the UL aggregation capability of the UE. Intypical TDD deployments, the number of CCs and the bandwidth of each CCin UL and DL is the same. A number of TAGs that can be configureddepends on the TAG capability of the UE.

CCs originating from the same eNB need not to provide the same coverage.

CCs shall be LTE Rel-8/9 compatible. Nevertheless, existing mechanisms(e.g., barring) may be used to avoid Rel-8/9 UEs to camp on a CC.

The spacing between center frequencies of contiguously aggregated CCsshall be a multiple of 300 kHz. This is in order to be compatible withthe 100 kHz frequency raster of Rel-8/9 and at the same time preserveorthogonality of the subcarriers with 15 kHz spacing. Depending on theaggregation scenario, the n×300 kHz spacing can be facilitated byinsertion of a low number of unused subcarriers between contiguous CCs.

For TDD CA, the downlink/uplink configuration is identical acrosscomponent carriers in the same band and may be the same or differentacross component carriers in different bands.

Dual connectivity is described.

FIG. 7 shows an example of dual connectivity to a macro cell and a smallcell. Referring to FIG. 7, the UE is connected to both the macro celland the small cell. A macro cell eNB serving the macro cell is the MeNBin dual connectivity, and a small cell eNB serving the small cell is theSeNB in dual connectivity. The MeNB is an eNB which terminates at leastS1-MME and therefore act as mobility anchor towards the CN in dualconnectivity. If a macro eNB exists, the macro eNB may function as theMeNB, generally. The SeNB is an eNB providing additional radio resourcesfor the UE, which is not the MeNB, in dual connectivity. The SeNB may begenerally configured for transmitting best effort (BE) type traffic,while the MeNB may be generally configured for transmitting other typesof traffic such as VoIP, streaming data, or signaling data. Theinterface between the MeNB and SeNB is called Xn interface. The Xninterface is assumed to be non-ideal, i.e., the delay in Xn interfacecould be up to 60 ms.

Power headroom according to the current specification of 3GPP LTE isdescribed. It may be referred to Section of 5.1.1.2 of 3GPP TS 36.213V11.3.0 (2013-06). There are two types of UE power headroom reportsdefined. A UE power headroom is valid for subframe i for serving cell c.

Type 1 power headroom is described. If the UE transmits PUSCH withoutPUCCH in subframe i for serving cell c, power headroom for a type 1report is computed using Equation 1.PH _(type1,c)(i)=P _(CMAX,c)(i)−{10 log₁₀(M _(PUSCH,c)(i))+P_(O_PUSCH,c)(j)+α_(c)(j)·PL _(c)+Δ_(TF,c) +f _(c)(i)}[dB]  <Equation 1>

In Equation 1, P_(CMAX,c)(i) is the configured UE transmit power insubframe i for serving cell c. M_(PUSCH,c)(i) is the bandwidth of thePUSCH resource assignment expressed in number of resource blocks validfor subframe i and serving cell c. P_(O_PUSCH,c)(j) is a parametercomposed of the sum of a component P_(O_NOMINAL_PUSCH,c)(j) providedfrom higher layers for j=0 and 1 and a component P_(O_UE_PUSCH,c)(j)provided by higher layers for j=0 and 1 for serving cell c. For j=0 or1, α_(c)∈{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} is a 3-bit parameterprovided by higher layers for serving cell c. For j=2, α_(c) (j)=1.PL_(c) is the downlink pathloss estimate calculated in the UE forserving cell c in dB.

If the UE transmits PUSCH with PUCCH in subframe i for serving cell c,power headroom for a type 1 report is computed using Equation 2.PH _(type1,c)(i)={tilde over (P)} _(CMAX,c)(i)−{10 log₁₀(M_(PUSCH,c)(i))+P _(O_PUSCH,c)(j)+α_(c)(j)·PL _(c)+Δ_(TF,c)(i)+f_(c)(i)}[dB]  <Equation 2>

In Equation 2, M_(PUSCH,c)(i), P_(O_PUSCH,c)(j), α_(c)(j), PLc aredefined in Equation 1. P⁻ _(CMAX,c)(i) is computed based on therequirements in 3GPP TS 36.101 assuming a PUSCH only transmission insubframe i. For this case, the physical layer delivers P⁻ _(CMAX,c)(i)instead of P_(CMAX,c)(i) to higher layers.

If the UE does not transmit PUSCH in subframe i for serving cell c,power headroom for a type 1 report is computed using Equation 3.PH _(type1,c)(i)={tilde over (P)} _(CMAX,c)(i)−{P_(O_PUSCH,c)(1)+α_(c)(1)·PL _(c) +f _(c)(i)}[dB]  <Equation 3>

In equation 3, P⁻ _(CMAX,c)(i) is computed assuming maximum powerreduction (MPR)=0 dB, additional MPR (A-MPR)=0 dB, power management MPR(P-MPR)=0 dB and ΔT_(C)=0 dB, where MPR, A-MPR, P-MPR and ΔT_(C) aredefined in 3GPP TS 36.101. P_(O_PUSCH,c)(1), α_(c)(1), PLc are definedin Equation 1.

Type 2 power headroom is described. If the UE transmits PUSCHsimultaneous with PUCCH in subframe i for the primary cell, powerheadroom for a type 2 report is computed using Equation 4.

                                     ⟨Equation  4⟩${{PH}_{{type}\; 2}(i)} = {{P_{{CMAX},c}(i)} - {10\log_{10}{\quad{\begin{pmatrix}{10^{{({{10{\log_{10}{({M_{{PUSCH},c}{(i)}})}}} + {P_{{O\;\_\;{PUSCH}},c}{(j)}} + {{\alpha_{c}{(j)}} \cdot {PL}_{c}} + {\Delta_{{TF},c}{(i)}} + {f_{c}{(i)}}})}/10} +} \\10^{{({P_{0\_\;{PUCCH}} + {PL}_{c} + {h{({n_{CQI},n_{HARQ},n_{SR}})}} + {\Delta_{F\;\_\;{PUCCH}}{(F)}} + {\Delta_{TxD}{(F^{\prime})}} + {g{(i)}}})}/10}\end{pmatrix}{\quad\lbrack{dB}\rbrack}}}}}$

In equation 4, P_(CMAX,c)(i), M_(PUSCH,c)(i), P_(O_PUSCH,c)(j),α_(c)(j), PL_(c) are the primary cell parameters as defined inEquation 1. P_(O_PUCCH) is a parameter composed of the sum of aparameter P_(O_NOMINAL_PUCCH) provided by higher layers and a parameterP_(O_UE_PUCCH) provided by higher layers. h(n_(CQI), n_(HARQ), n_(SR))is a PUCCH format dependent value, where n_(CQI) corresponds to thenumber of information bits for the channel quality information (CQI).n_(SR)=1 if subframe i is configured for SR for the UE not having anyassociated transport block for UL-SCH, otherwise n_(SR)=0=0. Theparameter Δ_(F_PUCCH)(F) is provided by higher layers. If the UE isconfigured by higher layers to transmit PUCCH on two antenna ports, thevalue of Δ_(T×D)(F′) is provided by higher layers. Otherwise,Δ_(T×D)(F′)=0.

If the UE transmits PUSCH without PUCCH in subframe i for the primarycell, power headroom for a type 2 report is computed using Equation 5.

                                     ⟨Equation  5⟩${{PH}_{{type}\; 2}(i)} = {{P_{{CMAX},c}(i)} - {10\log_{10}{\quad{\begin{pmatrix}{10^{{({{10{\log_{10}{({M_{{PUSCH},c}{(i)}})}}} + {P_{{O\;\_\;{PUSCH}},c}{(j)}} + {{\alpha_{c}{(j)}} \cdot {PL}_{c}} + {\Delta_{{TF},c}{(i)}} + {f_{c}{(i)}}})}/10} +} \\10^{{({P_{0\_\;{PUCCH}} + {PL}_{c} + {g{(i)}}})}/10}\end{pmatrix}{\quad\lbrack{dB}\rbrack}}}}}$

In Equation 5, P_(CMAX,c)(i), M_(PUSCH,c)(i), P_(O_PUSCH,c)(j),α_(c)(j), PL_(c) are the primary cell parameters as defined inEquation 1. P_(O_PUCCH) is defined in Equation 4.

If the UE transmits PUCCH without PUSCH in subframe i for the primarycell, power headroom for a type 2 report is computed using Equation 6.

                                     ⟨Equation  6⟩${{PH}_{{type}\; 2}(i)} = {{P_{{CMAX},c}(i)} - {10\log_{10}{\quad{\begin{pmatrix}{10^{{({{P_{{O\;\_\;{PUSCH}},c}{(1)}} + {{\alpha_{c}{(1)}} \cdot {PL}_{c}} + {f_{c}{(i)}}})}/10} +} \\10^{{({P_{0\_\;{PUCCH}} + {PL}_{c} + {h{({n_{CQI},n_{HARQ},n_{SR}})}} + {\Delta_{F\;\_\;{PUCCH}}{(F)}} + {\Delta_{TxD}{(F^{\prime})}} + {g{(i)}}})}/10}\end{pmatrix}{\quad\lbrack{dB}\rbrack}}}}}$

In equation 6, P_(O_PUSCH,c)(1), α_(c)(1), PLc are the primary cellparameters as defined in Equation 1. P_(CMAX,c)(i), P_(O_PUCCH),h(n_(CQI), n_(HARQ), n_(SR)), Δ_(F_PUCCH)(F), Δ_(T×D)(F′) are alsodefined in Equation 4.

If the UE does not transmit PUCCH or PUSCH in subframe i for the primarycell, power headroom for a type 2 report is computed using Equation 7.

$\begin{matrix}{{{PH}_{{type}\; 2}(i)} = {{{\overset{\sim}{P}}_{{CMAX},c}(i)} - {10\log_{10}{\quad{\begin{pmatrix}{10^{{({{P_{{O\;\_\;{PUSCH}},c}{(1)}} + {{\alpha_{c}{(1)}} \cdot {PL}_{c}} + {f_{c}{(i)}}})}/10} +} \\10^{{({P_{0\_\;{PUCCH}} + {PL}_{c} + {g{(i)}}})}/10}\end{pmatrix}{\quad\lbrack{dB}\rbrack}}}}}} & \left\langle {{Equation}\mspace{14mu} 7} \right\rangle\end{matrix}$

In Equation 7, P⁻ _(CMAX,c)(i) is computed assuming MPR=0 dB, A-MPR=0dB, P-MPR=0 dB and ΔT_(C)=0 dB, where MPR, A-MPR, P-MPR and ΔT_(C) aredefined in 3GPP TS 36.101. P_(O_PUSCH,c)(1), α_(c)(1), PLc are theprimary cell parameters as defined in Equation 1. P_(CMAX,c)(i),P_(O_PUCCH), h(n_(CQI), n_(HARQ), n_(SR)), Δ_(F_PUCCH)(F), Δ_(T×D)(F′)are defined in Equation 4.

The power headroom shall be rounded to the closest value in the range[40; −23] dB with steps of 1 dB and is delivered by the physical layerto higher layers.

Power headroom reporting (PHR) is described. It may be referred toSection of 5.4.6 of 3GPP TS 36.321 V11.3.0 (2013-06). Radio resourcecontrol (RRC) controls power headroom reporting by configuring the twotimers periodicPHR-Timer and prohibitPHR-Timer, and by signallingdl-PathlossChange which sets the change in measured downlink pathlossand the required power backoff due to power management (as allowed byP-MPR_(c)) to trigger a PHR.

A PHR shall be triggered if any of the following events occur:

-   -   prohibitPHR-Timer expires or has expired and the path loss has        changed more than dl-PathlossChange dB for at least one        activated serving cell which is used as a pathloss reference        since the last transmission of a PHR when the UE has UL        resources for new transmission;    -   periodicPHR-Timer expires;    -   upon configuration or reconfiguration of the power headroom        reporting functionality by upper layers, which is not used to        disable the function;    -   activation of an SCell with configured uplink.    -   prohibitPHR-Timer expires or has expired, when the UE has UL        resources for new transmission, and the following is true in        this TTI for any of the actived serving cells with configured        uplink: there are UL resources allocated for transmission or        there is a PUCCH transmission on this cell, and the required        power backoff due to power management (as allowed by P-MPR_(c))        for this cell has changed more than dl-PathlossChange dB since        the last transmission of a PHR when the UE had UL resources        allocated for transmission or PUCCH transmission on this cell.

If the UE has UL resources allocated for new transmission for this TTI:

1> if it is the first UL resource allocated for a new transmission sincethe last medium access control (MAC reset, start periodicPHR-Timer;

1> if the power headroom reporting procedure determines that at leastone PHR has been triggered and not cancelled, and;

1> if the allocated UL resources can accommodate a PHR MAC controlelement plus its subheader if extendedPHR is not configured, or theextended PHR MAC control element plus its subheader if extendedPHR isconfigured, as a result of logical channel prioritization:

2> if extendedPHR is configured:

3> for each activated serving cell with configured uplink:

4> obtain the value of the type 1 power headroom;

4> if the UE has UL resources allocated for transmission on this servingcell for this TTI:

5> obtain the value for the corresponding P_(CMAX,c) field from thephysical layer;

3> if simultaneousPUCCH-PUSCH is configured:

4> obtain the value of the type 2 power headroom for the PCell;

4> if the UE has a PUCCH transmission in this TTI:

5> obtain the value for the corresponding P_(CMAX,c) field from thephysical layer;

3> instruct the multiplexing and assembly procedure to generate andtransmit an extended PHR MAC control element based on the valuesreported by the physical layer;

2> else:

3> obtain the value of the type 1 power headroom from the physicallayer;

3> instruct the multiplexing and assembly procedure to generate andtransmit a PHR MAC control element based on the value reported by thephysical layer;

2> start or restart periodicPHR-Timer;

2> start or restart prohibitPHR-Timer;

2> cancel all triggered PHR(s).

A power headroom MAC control element (CE) and an extended power headromMAC CE are described. It may be referred to Section of 6.3.1.6 of 3GPPTS 36.321 V11.3.0 (2013-06).

The power headroom MAC CE is identified by a MAC protocol data unit(PDU) subheader with logical channel identifier (LCID) having a value of11010. It has a fixed size and consists of a single octet.

FIG. 8 shows a power headroom MAC CE. Referring to FIG. 8, the powerheadroom MAC CE defined as follows:

-   -   R: reserved bit and set to “0”.    -   PH: this field indicates the power headroom level. The length of        the field is 6 bits. The reported PH and the corresponding power        headroom levels are shown in Table 1 below.

TABLE 1 PH Power Headroom Level  0 POWER_HEADROOM_0  1 POWER_HEADROOM_1 2 POWER_HEADROOM_2  3 POWER_HEADROOM_3 . . . . . . 60 POWER_HEADROOM_6061 POWER_HEADROOM_61 62 POWER_HEADROOM_62 63 POWER_HEADROOM_63

The extended power headroom MAC CE is identified by a MAC PDU subheaderwith LCID having a value of 11001. It has a variable size.

FIG. 9 shows an extended power headroom MAC CE. Referring to FIG. 9,when Type 2 PH is reported, the octet containing the type 2 PH field isincluded first after the octet indicating the presence of PH per sCelland followed by an octet containing the associated P_(CMAX,c) field (ifreported). Then follows in ascending order based on the ServCellIndex anoctet with the type 1 PH field and an octet with the associatedP_(CMAX,c) field (if reported), for the PCell and for each SCellindicated in the bitmap.

The extended power headroom MAC CE is defined as follows:

-   -   C_(i): this field indicates the presence of a PH field for the        SCell with SCellIndex i. The C_(i) field set to “1” indicates        that a PH field for the SCell with SCellIndex i is reported. The        C_(i) field set to “0” indicates that a PH field for the SCell        with SCellIndex i is not reported.    -   R: reserved bit, set to “0”.    -   V: this field indicates if the PH value is based on a real        transmission or a reference format. For type 1 PH, V=0 indicates        real transmission on PUSCH and V=1 indicates that a PUSCH        reference format is used. For type 2 PH, V=0 indicates real        transmission on PUCCH and V=1 indicates that a PUCCH reference        format is used. Furthermore, for both type 1 and type 2 PH, V=0        indicates the presence of the octet containing the associated        P_(CMAX,c) field, and V=1 indicates that the octet containing        the associated P_(CMAX,c) field is omitted.    -   PH: this field indicates the power headroom level. The length of        the field is 6 bits. The reported PH and the corresponding power        headroom levels are shown in Table 1 described above.    -   P: this field indicates whether the UE applies power backoff due        to power management (as allowed by P-MPR_(c)). The UE shall set        P=1 if the corresponding P_(CMAX,c) field would have had a        different value if no power backoff due to power management had        been applied.    -   P_(CMAX,c): if present, this field indicates the P_(CMAX,c) or        P⁻ _(CMAX,c) used for calculation of the preceding PH field. The        reported P_(CMAX,c) and the corresponding nominal UE transmit        power levels are shown in Table 2.

TABLE 2 P_(CMAX,c) Nominal UE transmit power level  0 PCMAX_C_00  1PCMAX_C_01  2 PCMAX_C_02 . . . . . . 61 PCMAX_C_61 62 PCMAX_C_62 63PCMAX_C_63

Hereinafter, a method for transmitting a power headroom according toembodiments of the present invention is described. An embodiment of thepresent invention may consider a case where inter-site carrieraggregation is used for a UE. Inter-site carrier aggregation may bedefined as that a UE is configured with multiple carriers where at leasttwo carriers are associated with separate eNBs which may be connected byideal backhaul or non-ideal backhaul. When a UE can perform simultaneoustwo UL transmissions (including PUSCH/PUCCH), the following cases may beconsidered.

-   -   Case 1: FDD+FDD or same DL/UL configuration TDD+TDD over idea        backhaul    -   Case 2: FDD+FDD or same DL/UL configuration TDD+TDD over        non-idea backhaul    -   Case 3: FDD+TDD or different DL/UL configuration TDD+TDD over        ideal backhaul    -   Case 4: FDD+TDD or different DL/UL configuration TDD+TDD over        non-ideal backhaul

When a UE cannot be able to perform simultaneous two UL transmissions,the following cases may be considered.

-   -   Case 5: FDD+FDD or same DL/UL configuration TDD+TDD over idea        backhaul    -   Case 6: FDD+FDD or same DL/UL configuration TDD+TDD over        non-idea backhaul    -   Case 7: FDD+TDD or different DL/UL configuration TDD+TDD over        ideal backhaul    -   Case 8: FDD+TDD or different DL/UL configuration TDD+TDD over        non-ideal backhaul

Hereinafter, for the convenience, a case where more than one carriergroup is configured by a single eNB where each carrier group may have acarrier receiving PUCCH is called “PUCCH offloading”. Each carrier groupmay have multiple carriers, even though the number of PUCCH carrier maybe limited to only one per carrier group.

According to an embodiment of the present invention, power headroom maybe calculated per CC, and all calculated power headroom may be reportedto two eNBs. In addition to power headroom for each CC, eNBs mayexchange its configured P_(CMAX,eNB) _(j) (i) with each other or the UEmay inform the value to other eNB. When the UE configured with more thanone P_(CMAX,c)(i), power headroom may be calculated per each configuredP_(CMAX,c)(i) and then may be reported to eNBs. More specifically, ifthe UE is configured with more than one maximum power usable for morethan one subsets of subframes where the maximum power value is appliedper each subset of subframe, power headroom may be calculated using themaximum power assigned to that specific subframe and may be reported.Additionally, more than one values with all configured maximum powersmay be reported as well. Alternatively, one power headroom may bereported depending on where the PHR has been triggered. For example, ifPHR is triggered at a subframe with low power configured, low power maybe used for calculating PHR. If PHR is triggered at a subframe with highpower configured, higher power may be used for calculating PHR.

When PHR is calculated, whether to use P_(CMAX,c)(i) or P_(CMAX,eNB)_(j) (i) as a maximum power per carrier may be considered. One option isto use P_(CMAX,c)(i) regardless of P_(CMAX,eNB) _(j) (i) such that eacheNB knows the power budget regardless of the allocated power for eacheNB. This would be useful when power is shared between two eNBs, yet,power scaling may be occurred within a carrier group only per theallocated power. Alternatively, min {P_(CMAX,c)(i), P_(CMAX,eNB) _(j)(i)} may be used to calculate PHR. In this case, this may limit theamount of power increased from an eNB perspective. Thus, this may bemore aligned with approach where power scaling/limit is determined percarrier group and unused power may be used by the other eNB. Anotheralternative is to use P_(CMAX) regardless of P_(CMAX,c)(i) orP_(CMAX,eNB) _(j) (i) such that each eNB knows how much power has beenactually allocated to each carrier.

In detail, for each option, PHR reporting behaves as follows. Assumingthat the UE reports PHR on all activated carrier with UL configured, itwill be further assumed that for carrier where PUCCH is transmitted,type 2 PHR reporting is mandated regardless of PUCCH/PUSCH simultaneoustransmission capability/configurability. However, this may be applied toa case where type 2 PHR reporting is not mandated or not used.

1) Option 1: Use P_(CMAX,c)(i)—This value may be used to calculate PHR.This may correspond to the current specification described above.

2) Option 2: Use P_(CMAX,eNB) _(j) (i)—instead of P_(CMAX,c), this valuemay be used to calculate PHR. However, since the eNB can estimate thePHR between P_(CMAX,eNB) _(j) (i) and accumulated power based onP_(CMAX,c)(i), this option is not desirable. One way to estimate PHR forP_(CMAX,eNB) _(j) (i) may be that “PHR+{P_(CMAX,eNB) _(j(i))−P_(CMAX,c)}” where two values are higher layer configured.

3) Option 3: Use P_(CMAX)—this may be similar to option 2. This valuecan be calculated using PHR based on P_(CMAX,c)(i).

Thus, overall, it is desirable to use P_(CMAX,c)(i) for calculating PHR.

Another approach of reporting power headroom in a dual connectivityscenario is to define new reporting class, namely, class A and class B.The class A may be determined based on the assumption that simultaneousuplink transmission occur between two connections. The class B may bedetermined based on the assumption that only one uplink transmissionoccurs to the serving cell. For example, if FDD and TDD carriers areaggregated, and then one value of P_(CMAX,c) is configured for eachserving cell, to manage different uplink subframes where potentiallyonly one uplink transmission occurs because TDD configuration definesdownlink subframe in that specific time frame and some other subframescan potentially have two or more simultaneous uplink transmissions,different power headroom reporting classes may be specified. If this isused, it may be also considered to use two (or more) independent uplinkpower control loops. When more than two carriers are aggregated, theclass A and B may be determined only between PCell and super SCell.

Assuming a scenario that more than one eNBs configure inter-noderesource aggregation for a UE, it may be assumed that the UE reports PHRof each configured serving cell configured by an eNB to the eNBrespectively. For example, two eNBs, i.e., eNB1 and eNB2, configure CC1,CC2 and CC3, CC4 respectively. The UE then reports PHR of CC1 and CC2 tothe eNB1 and CC3 and CC4 to the eNB2 respectively. When the UEcalculates the PHR, the measured maximum power may be calculated inconsideration of other eNBs.

One example of calculating P_(CMAX) would be to subtract power used forthe other eNB (sum of PUSCH power to CCs configured by the other eNB) asshown in Equation 8 below.

$\begin{matrix}{{{\overset{\sim}{P}}_{{CMAX},c}(i)} = {{{\overset{\sim}{P}}_{{CMAX},c}(i)} - {\sum\limits_{j \neq c}^{\;}{{\hat{P}}_{{PUSCH},j}(i)}}}} & \left\langle {{Equation}\mspace{14mu} 8} \right\rangle\end{matrix}$

Or, only PUSCH power to super SCell may be extracted in calculating themaximum power. If the other eNB cannot schedule uplink (e.g., configuredas downlink subframe in the given subframe), the subframe would not beoccurred. Thus, depending on where the PHR is reported (and calculated),serving eNB may estimate maximum power configurable per subframeconfiguration.

Another approach of reporting power headroom in a dual connectivityscenario is to configure one or more than one PHR configurations pereach eNB or each carrier group. Power headroom is calculated for allactivated with uplink configured per each instance of PHR reporting. Inother words, the calculated power headroom for each carrier may betransmitted to both eNBs. Calculated PHR may be reported to each eNBfollowing individual configuration.

Table 3 shows change of power headroom.

TABLE 3 Simultaneous PUCCH/PUSCH PCell SCell (T1, P_(CMAX) Real), (T1,P_(CMAX)) No, No PUSCH x (T1, P_(CMAX) Real), (T1, P_(CMAX)), Yes, YesPUSCH x (T2, P_(CMAX)), (T2, P_(CMAX)) (T1, P_(CMAX) Real), (T1,P_(CMAX) No, No PUSCH PUSCH Real) (T1, P_(CMAX) Real), (T1, P_(CMAX)Yes, Yes PUSCH PUSCH Real) (T2, P_(CMAX)), (T2, P_(CMAX)) (T1,P_(CMAX)), (T1, P_(CMAX)) No, No PUCCH x (T1, P_(CMAX)), (T1, P_(CMAX)),(T2, Yes, Yes PUCCH x P_(CMAX) Real), (T2, P_(CMAX)) (T1, P_(CMAX)),(T1, P_(CMAX) Real) No, No PUCCH PUSCH (T1, P_(CMAX) Real), (T1,P_(CMAX)) Yes, Yes PUSCH PUCCH (T2, P_(CMAX)), (T2, P_(CMAX))

Indicating actual transmission of PUCCH or PUSCH (or indication of realP_(CMAX) or virtual P_(CMAX) when reporting to higher layer for servingcell) may be necessary when aggregated PHRs are reported to both eNBsfor all activated cells with uplink configured. To minimize theoccurrence where the UE reports virtual P_(CMAX) (i.e., assuming noMPR), it may be assumed that when there is no PUSCH or PUCCH scheduledat a subframe where the reporting occurs, the UE may assume that adefault configuration is used for PUSCH or PUCCH transmission (i.e.,default resource allocation is assumed to calculate maximum power) andthe UE may report PHR and the calculated P_(CMAX) for each serving cell.

For each carrier where PUCCH can be transmitted, type 1 PH and type 2 PHmay be generated depending on PUCCH/PUSCH simultaneous transmissionconfiguration.

When PHRs are reported for both eNBs for all activated carriers, thereare cases where type 1 PH is reported with virtual P_(CMAX) (i.e., basedon not accounting for actual schedule and MPR values) when PUCCHtransmission occurs only in a carrier. As virtual P_(CMAX) becomesunclear considering the allocated/used power to PUCCH to the second eNBwhich does not have any scheduling information of the first eNB, atleast, the flag to indicate whether PUCCH has been transmitted or notmay be added such that the second eNB knows how the power headroom iscalculated for the first eNB.

Or, when dual connectivity is configured, regardless of PUCCH/PUSCHsimultaneous transmission capability and/or regardless of whethersimultaneous PUCCH/PUSCH transmission is configured or not, the UE maybe requested to report both type 1 PH and type 2 PH for at leastcarriers which can transmit PUCCH. More specifically, this may beapplied for carriers configured by the first eNB when power headroom isreported to the second eNB. Likewise, this may be applied for carriersconfigured by the second eNB when power headroom is reported to thefirst eNB.

FIG. 10 shows an example of a method for transmitting a PHR according toan embodiment of the present invention. In step S100, the UE transmits afirst PHR for a first carrier group to a second carrier group. In stepS110, the UE transmits a second PHR for the second carrier group to thefirst carrier group. The first PHR transmitted to the second carriergroup and the second PHR transmitted to the first carrier group mayinclude a PHR for PUSCH transmission (i.e., type 1 PHR) and a PHR forPUCCH transmission (i.e., type 2 PHR) regardless of whether simultaneoustransmission of PUCCH/PUSCH is configured or not in dual connectivityand/or multiple carrier groups. That is, PHR for carriers configured bythe second eNB which are transmitted to the first eNB may be based onboth type 1 PHR and type 2 PHR, regardless of the configuration ofPUCCH/PUSCH simultaneous transmission in carrier group of the second eNBand/or regardless of the UE capability to support PUCCH/PUSCHsimultaneous transmission capability. PHR for carriers configured by thefirst eNB which are transmitted to the first eNB and PHR for carriersconfigured by the second eNB which are transmitted to the second eNB maybe based on only type 1 PHR according to the current specification. TheUE may further transmit P_(CMAX,c) which is configured UE transmit powerfor serving cell c. The first carrier group may correspond to an MeNB indual connectivity, and the second carrier group may correspond to anSeNB in dual connectivity. The first carrier group may include aplurality of CCs, and the second carrier group includes a plurality ofCCs.

If the UE actually transmits PUCCH in a specific cell, the UE mayfurther transmit an indication which indicates that the PHR/P_(CMAX,c)corresponds to the PUCCH transmission or that PUCCH is actuallytransmitted. If the UE reduces transmission power of PUCCH/PUSCH in aspecific cell due to transmission of other cells, the UE may furthertransmit an indication indicating that fact. One candidate is to triggerPHR so that it can give very minimum power headroom value or evennegative power headroom value to eNBs.

It is also considered to trigger PHR when power related configurationoccurs. For example, if the MeNB configures power split between the MeNBand SeNB, the UE may be triggered with PHR reporting so that it mayreport the usable PHR value properly. Further, regardless of powerconfiguration, when the SeNB configures (or after successful connectionwith the SeNB), the UE may also reports PHR. This implies that when theMeNB configures pSCell (PUCCH cell on SCG), the UE may report PHR.Besides, when the SeNB and/or MeNB activate a carrier, PHR may betriggered.

FIG. 11 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

An eNB 800 may include a processor 810, a memory 820 and a radiofrequency (RF) unit 830. The processor 810 may be configured toimplement proposed functions, procedures and/or methods described inthis description. Layers of the radio interface protocol may beimplemented in the processor 810. The memory 820 is operatively coupledwith the processor 810 and stores a variety of information to operatethe processor 810. The RF unit 830 is operatively coupled with theprocessor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method performed by a first base station in awireless communication system with dual connectivity, the methodcomprising: receiving, by the first base station from a wireless device,a type 1 power headroom for all activated carriers related to the firstbase station and all activated carriers related to a second basestation; and receiving, by the first base station from the wirelessdevice, a type 2 power headroom for a carrier in which a physical uplinkcontrol channel (PUCCH) for the second base station can be transmittedto the second base station, wherein the wireless device is connected toboth the first base station and the second base station in the dualconnectivity.
 2. The method of claim 1, wherein the type 2 powerheadroom is always received regardless of whether simultaneoustransmission of the PUCCH for the second base station and a physicaluplink shared channel (PUSCH) for the second base station is configuredor not.
 3. The method of claim 1, wherein the first base station is amaster node in the dual connectivity, and wherein the second basestation is a secondary node in the dual connectivity.
 4. The method ofclaim 1, wherein the first base station is a secondary node in the dualconnectivity, and wherein the second base station is a master node inthe dual connectivity.
 5. The method of claim 1, wherein the wirelessdevice is configured with simultaneous transmission of a PUCCH for thefirst base station and a PUSCH for the first base station.
 6. The methodof claim 5, further comprising: receiving a type 2 power headroom for acarrier in which a PUCCH for the first base station can be transmittedto the first base station from the wireless device.
 7. The method ofclaim 1, further comprising: receiving P_(CMAX,c), which is a configureduser equipment (UE) transmit power for serving cell, from the wirelessdevice.
 8. The method of claim 1, further comprising: receiving anindicator, which indicates that the carrier for which the type 2 powerheadroom is received actually transmits the PUCCH for the second basestation, from the wireless device.
 9. A first base station (BS) in awireless communication system with dual connectivity, the first BScomprising: a memory; a radio frequency (RF) unit including atransceiver; and a processor, operably coupled to the memory and the RFunit, wherein the first BS is configured to: receive a type 1 powerheadroom for all activated carriers related to the first base stationand all activated carriers related to a second base station from awireless device, and receive a type 2 power headroom for a carrier inwhich a physical uplink control channel (PUCCH) for the second basestation can be transmitted to the second base station from the wirelessdevice, wherein the wireless device is connected to both the first basestation and the second base station in the dual connectivity.
 10. Thefirst BS of claim 9, wherein the type 2 power headroom is alwaysreceived regardless of whether simultaneous transmission of the PUCCHfor the second base station and a physical uplink shared channel (PUSCH)for the second base station is configured or not.
 11. The first BS ofclaim 9, wherein the first base station is a master node in the dualconnectivity, and wherein the second base station is a secondary node inthe dual connectivity.
 12. The first BS of claim 9, wherein the firstbase station is a secondary node in the dual connectivity, and whereinthe second base station is a master node in the dual connectivity. 13.The first BS of claim 9, wherein the wireless device is configured withsimultaneous transmission of a PUCCH for the first base station and aPUSCH for the first base station.
 14. The first BS of claim 13, whereinthe first BS is further configured to receive a type 2 power headroomfor a carrier in which a PUCCH for the first base station can betransmitted to the first base station from the wireless device.
 15. Thefirst BS of claim 9, wherein the first BS is further configured toreceive P_(CMAX,c), which is a configured user equipment (UE) transmitpower for serving cell, from the wireless device.
 16. The first BS ofclaim 9, wherein first BS is further configured to receive an indicator,which indicates that the carrier for which the type 2 power headroom isreceived actually transmits the PUCCH for the second base station, fromthe wireless device.
 17. A processor for a first base station (BS) in awireless communication system with dual connectivity, wherein theprocessor is configured to control the first base station to: receive atype 1 power headroom for all activated carriers related to the firstbase station and all activated carriers related to a second base stationfrom a wireless device, and receive a type 2 power headroom for acarrier in which a physical uplink control channel (PUCCH) for thesecond base station can be transmitted to the second base station fromthe wireless device, wherein the wireless device is connected to boththe first base station and the second base station in the dualconnectivity.